1. Field
Aspects of the present disclosure relate generally to a method and system for treating osteoarthritis with electromagnetic stimulation and/or ultrasound.
2. Background
Osteoarthritis (OA) of the knee is the most common form of OA affecting more than ten million Americans and is the most common cause of disability in the United States. Symptoms may include pain, stiffness, limited range of motion and localized swelling. Currently, there is no known cure for OA and current treatments are intended to mitigate the symptoms.
As shown in FIG. 1, the human knee is a synovial joint between the femur and tibia. The joint is contained within a fibrous joint capsule with a synovial membrane lining. The ends of the bones are covered with articular cartilage and the bone beneath the cartilage is the subchondral bone. Hyaline articular cartilage loss is the central signature event in OA. While the exact etiology of OA is unknown, the pathophysiology involves a combination of mechanical, cellular, and biochemical processes.
With reference to FIG. 2, there are three primary types of bone: woven bone, cortical bone, and cancellous bone. Woven bone is found during fracture healing (callus formation). Cortical bone, also called compact or lamellar bone, is remodeled from woven bone and forms the internal and external tables of flat bones and the external surfaces of long bones. Cancellous bone (trabecular bone) lies between cortical bone surfaces and consists of a network of honeycombed interstices containing hematopoietic elements and bony trabeculae. The trabeculae are predominantly oriented perpendicular to external forces to provide structural support.
Bone remodeling is the process by which bone is renewed to maintain bone strength and mineral homeostasis. Remodeling involves continuous removal of discrete packets of old bone, replacement of these packets with newly synthesized proteinaceous matrix, and subsequent mineralization of the matrix to form new bone. The remodeling process resorbs old bone and forms new bone and cancellous bone is continually undergoing remodeling on the internal endosteal surfaces.
There is a vascular component which is integrally associated with the process of bone remodeling. This vascular contribution has both an anatomic basis and functional relevance. The subchondral region is highly vascular with terminal vessels in direct contact with the deepest hyaline cartilage layer. Bone remodeling occurring in a bone chamber is also related to the existence of and increased flow through microvessels that conform closely to the contour of the cancellous bone surface. Pericytes are intimately involved in the process of angiogenesis which accompanies the vascular component involved with cancellous bone remodeling. The microvasculature has been linked to the regulation of coupling between bone resorption and bone formation. This structure forms the anatomic basis for the knowledge that the vascular system is associated with osteogenesis during bone remodeling.
Cellular changes have been identified in osteoarthritis of the knee to include bone marrow edema, extensive intertrabecular fibrosis and sclerosis, as well as vascularization and thickening of the trabeculae in the subchondral bone. These combine to increase the stiffness of the subchondral bone, transmitting increased load to the overlying cartilage and leading to secondary cartilage damage. The increased venous vascular resistance contributes to venous congestion, increased intraosseous pressure, congestive bone pain, diminished nutrient delivery and progression of the disease. There is an interrelationship between cartilage damage and subchondral bone integrity.
The current understanding of the pathogenesis of OA has led the American Academy of Orthopaedic Surgeons (AAOS) to develop recommendations for treatment of knee OA. These include activity modification, weight loss, fitness, range of motion and quadriceps strengthening exercises, patellar taping, acupuncture, glucosamine, NSAIDS, acetaminophen, analgesics, and injections of intra-articular corticosteroids or hyaluronic acid. Surgical treatments include arthroscopy, meniscectomy, osteotomy and knee replacement surgery. In this context, there is a need for an enhanced method for treating OA in a noninvasive manner.